Are we mature by 18? - CrowdScience podcast, BBC World Service

What changed when you turned 18? More responsibilities and like, you know,  just feeling like you're not a kid anymore, you know, you have like things you have to  pay for and like things you have to like take care of with the government  and fear of like growing older. Meet friends Marla, Milou and Clara, who  recently reached the ripe old age of 18.

Very excited because I've been waiting to  turn 18 for a very long time of course. I could finally like go out and get drinks  and stuff like that so it's very fun. I've been so excited and it's finally there.

I was excited about being able to show my  ID because now I can get in wherever I want. Normally when you're 17 and you want to  get a drink you have to like play dumb and like "oh no I forgot my ID" and  now I'm like I am actually 18. Yeah.

So I feel very proud when I'm buying cigarettes or drinks like I feel very mature but. . . 

Do you feel mature in any other ways? Do we? Yeah I don't even  know how to do the laundry, so like how am I supposed to live by myself?

You're listening to CrowdScience from the  BBC World Service. I'm Caroline Steel and that was a little insight into how mature  three teenagers from Mexico, England and the Netherlands feel now that they're 18. I should also say that CrowdScience does not condone underage drinking or smoking  and neither does Marla's dad Richard, who also happens to be the producer of this show.

Anyway the reason Richard asked his daughter about entering adulthood is because of a question we're  tackling in this episode from listener Lynda. Hi, so I'm Lynda. I'm currently living  in the UK.

I'm originally from Algeria. My question for CrowdScience is: 'I'm  wondering why 18 years old is determined as the age of maturity? " This question has been on Lynda's mind for a while because when she was  18, her maturity was really put to the test.

I was at University in Algeria and students  used to strike for different reasons and there is one day where there is a strike, but not  all the students wanted to strike. A few of them they want to attend the lectures and  there was a student from the committee he came and he explained the reason why they  are striking and everything. Actually I was convinced by the explanation.

So a few students they were also convinced so they left the lecture.  A few they were not so they stayed. And for me I was convinced but at the same time I  wanted to attend the lecture so I think there are a few people like me.

So we were standing there  in the middle and then the professor said, "Well I'm fine with the people who left, I'm fine  with the who stay here, I think the worst thing in the life is the people standing the middle". And I was a good student and I had a lot of respect for the professors, so I was so  ashamed. I said, so it is you always need to take a decision.

And not taking a decision is  very bad. It's worse than making a bad decision. So it was like the point that I decided in the  future I was taking the decision for things.

Do you think that was a bit of a turning  point? Did you become more decisive after that? Yeah, so I think we need experience in life to  be able to learn and make decisions and mature.

There is a cultural aspect and this affects  a lot the behaviour of people but I think no matter where we are I think we have the  same, humans. So same physiology. So I'm wondering if we are mentally and also physically  mature at 18, especially the brain part of it.

Thanks Lynda. To be honest I think your lecturer  was quite harsh there. That's a difficult decision to make and I can think of countless times in my  late teenage years where I made categorically the wrong choice.

But was I doomed to get it wrong? Maybe our brains and bodies just aren't ready for good decision- making at 18. And why is 18 the age of maturity in most countries anyway?

Although  interestingly in Algeria, where Lynda's from, it's actually 19. But regardless of the number,  with reaching the age of maturity you are legally considered an adult, which may come with the  right to vote, get married or buy alcohol, amongst others, but from a science point of  view is 18 really the start of adulthood? Well the age of maturity being set at  18, as it is in most countries actually, that decision was made long before we knew  anything about the development of the brain.

This is Sarah-Jayne Blakemore.  Professor of Psychology and Cognitive Neuroscience at Cambridge University. She's an expert on how our  brain develops with age, so I'm hoping she can tell us  when our brains fully mature.

That is a really good question and it sounds  like a question that should have an obvious answer but unfortunately it doesn't. It's  a very complicated question because we don't really know what a fully mature brain  looks like. There are two reasons for that.

First of all it's only really in the last 20  years that we have been able to look at the development of the living human brain using  brain scanning technology like MRI so we're only really quite recently learning about how  the brain develops throughout childhood and adolescence and into early adulthood. And the  second reason is that the adult brain is still changing. So our brains are plastic.

That means  they adapt to the environment which allows us to learn new information and acquire new knowledge.  There is no age limit to that neuroplasticity. So if I showed you two brain scans you  wouldn't necessarily be able to say you know that's the brain of a 30-year-old and  that's the brain of a 20-year-old?

I can tell you that that would be at the  moment an impossible task for a human to do. So if you showed me, even though there is a  difference on average if you scan lots of people there is a difference between a 20-year-old  brain and a 30-year old brain, on average, even as someone who scans the brain I wouldn't  be able to tell the difference. Now that's not to say that at some point we won't be able  to tell the difference but at the moment that is not possible.

That's partly because overall there  is not much difference between a 20-year-old and a 30-year-old brain. For example they're the same  size, the same volume overall. In fact the human brain becomes about adult size by about age  eight or nine years, so by about nine years the brain is adult size and it doesn't change  its overall size or volume very much at all.

What changes is the composition of the  brain. For example, the amount of gray matter and the amount of white matter,  which undergoes very substantial changes after age nine right throughout  adolescence and into early adulthood. So there's not sort of, I don't know,  something special that happens to your brain when you turn 18 and you're suddenly,  supposedly a complete adult?

It's not like, ah that's the average age that your prefrontal  cortex stops developing, or something like that? There isn't a sort of neuroscience  reason for 18 to be the age of maturity? So the brain is still developing at 18 in the  vast majority of young people.

Their brains will still continue to develop in terms of the  internal composition of white matter and gray matter for example, right throughout  the late teens and into the twenties. Interestingly we've only known  that the brain develops during adolescence and into early  adult in the last 20 years. When I was an undergraduate, 30 years ago, I was taught that the human brain  stops developing in childhood.

I remember being taught that and I also kept  my undergraduate textbooks and that's exactly what they say. So interestingly, when the legal  age of adulthood was set at 18 many, many decades ago that was decades before we knew that the  brain continues to develop after childhood. So it had that decision about the age of legal  maturity had nothing to do with neuroscience.

So now we do know about the development of  the brain, you know, does the neuroscience somehow follow the legal decision about the  age of maturity? Not much. In terms of their prefrontal cortex you mention, that's the  part of the brain that is responsible for things like decision-making and planning and  stopping yourself doing something inappropriate or for example illegal, it's also involved in  things like self-awareness and social cognition, understanding other people's minds, that  region of the brain is one of the latest regions to mature, continues to develop  right throughout the teens and the twenties.

As do the cognitive functions that rely on  the prefrontal cortex. So there's cognitive functions I just mentioned like decision-making  and planning and inhibition, self-regulation, they all continue to develop right throughout  the teens and start to plateau into the twenties. So for most people those abilities start  to sort of become fully mature in the early twenties but there's nothing special  that happens at 18 in everyone's brain.

That's so interesting. If, you know, part  of our brain which is responsible for good decision-making in most people hasn't fully  developed until at least their twenties, it sort of feels like how can we expect  18-year-olds to be making sensible decisions. Well, by 18 most people's executive  functions, that's the collective name for these cognitive processes like decision-making  and planning and and inhibiting inappropriate responses, most people's executive functions are  doing pretty well in terms of how they perform on these tasks.

So I think we can for most  people expect them to be able to make good decisions by around 18 but the main point  here is that there are very big individual differences in that. So some people's  executive functions stop improving in the mid-teens and other people's continue  to develop until the mid twenties. So, maybe you feel like listener Lynda and me and  you didn't, don't or won't feel mature at 18.

Or you might have been making your best decisions  at just 15. Our brains are all different which makes it difficult to come up with laws linked  to maturity. So perhaps it's unsurprising that different countries have drawn the line at  different ages.

And the cultural contrasts aren't just legal. There are also variations  in the ages adult milestones tend to happen, like marrying or having children. In Algeria where listener Lynda comes from, the average age of first marriage is 32.

In some  countries, like Liberia, it's as low as 21 and India sits somewhere in the middle at 28. Maybe  the age we choose to do grown-up things could be a clue as to when and why we're really mature. To help me find out more I'm joined by Chhavi Sachdev.

She's a Mumbai-based journalist  and friend of CrowdScience - hi Chhavi! Welcome. Hello Caroline.

Thank you  for joining us.  Always a pleasure. So, when are people in India seen as mature enough  to get married and have children?

So, this is a difficult question to answer but legally, like  you were talking about with different countries, in India until 1978 it used to be that girls  could get married at 14 and boys at 18 and then less than 50 years ago this was changed. Girls can  get married at 18 now and the boys have to be 21. So what kind of age do people start  feeling pressure to get married and or have children?

I guess it must vary region  to region but are there any sort of patterns? So I think traditionally there is a sense that  you have certain stages of life and you have roles you need to perform. So when you finished  studying the next thing you need to do if you're a boy is get a job, become stable enough to  support a family and then start that family.

For girls you study and then if you're from a  family or a society that believes your role is really as a homemaker and the mother of society  so you need to have children, then off you go and start that phase of your life. If I'm not being too nosy have you felt these pressures? So I am definitely an exception and an outlier even in my own extended family, and  that's partly because my parents were exceptions.

Back when I was in school it was a thing that  everybody in my classes was amazed at that my parents had what we call a love marriage. It  was not an arranged match, they chose each other. And my mother was over the hill compared  with other people, she was in her twenties.

She got an advanced degree and married for love. She was in her twenties, I love how that's old! Yeah I don't know if she'd appreciate  my telling everybody who's listening, but she was 25 and that like  you know her chances were over, she was on the shelf.

But she knew what she  was doing. They also really espoused having a choice and finding your own life partner.  So while my classmates were introduced to a lot of people or their marriages were set up for  them, I was exempt.

But obviously that's just my experience and as I've said I'm an exception. I  also spoke to Amrita, who grew up in a smaller, more conservative town, about her experience. Hi, I'm Amrita.

I'm almost 49 years old and I was 22 when I had my first child. I  turned 20 right after I got married. 18, I think I was in school just about to give  my board exams and after that I joined college.

But I never did get to finish it because I got  married when I was in my second year of college. So there was a lot of pressure on me to do  the right thing at it, as it was called. So I did have a choice, but it was not much of  a choice.

You know at 18, at even 19 or 20, I don't think I had the maturity or even the knowledge or the self-awareness  to take any kind of decision. I don't know what, you know, reservoirs of  strength I tapped into to bring my kids up, but I think I was too immature and I did not have the emotional strength  to be a very levelheaded mother. I don't think women should have children  before they're 26 years old at least.

My daughter has just crossed 26 and I now feel that, yes, she's prepared for motherhood, for  marriage, for a complex relationship. It's interesting that Amrita says she  sees her daughter being mature at 26. I'm 30 and I still think I'm nowhere near mature enough to have children.

But I guess  it really varies culture to culture. I agree. And I also spoke to another woman, Manju, who's from a village four hours away from  Mumbai where I live.

She had her first child even earlier and her concerns  were more about physical maturity. So I was 17 when I had my first child. Do you look back and think that  was the right age to have a child?

No, no it wasn't. She said it would have been better if she  was 23 or 24 when she'd had a child. Why?

Everything was hurting her knees, her  back and it was a lot of pain and trouble. She says when you're older, like 23, 24,  you finish growing, your bones are stronger, your body is stronger and then  you have the strength to chase after your children and when you're that  young at 16, 17, you don't have that. You’re listening to CrowdScience from the BBC  World Service.

I’m Caroline Steel and in this episode we’re looking into listener Lynda’s  question about when we become mature - and whether 18, the age of legal adulthood in  most countries, has any scientific basis. We’ve just heard from Amrita  and Manju in India about their experience of becoming mothers  for the first time at 22 and 17. Amrita didn’t feel emotionally mature,  which makes sense - we heard earlier from neuroscientist Sarah Jane that  some people’s brains aren’t fully developed well into their twenties. 

But what about our physical maturity? It really depends which kind of maturation,  even which kind of biological maturation. This is Barry Bogin, leading  biological anthropologist and author of a book called Patterns of Human Growth.

Well, my special interest is  human physical growth, height, weight, muscle fat and also reproductive maturity. All those things are already going  on before we're born. You know, foetuses are growing and  even maturing in many ways.

For instance, our sexual maturation stops just about at birth and doesn't  even pick up again until puberty. On average, about age nine  is when it starts up again and really gets going at ten, 12 years of age. If we look at height, girls, young women more or  less finish growing in height by about 17 or 18.

Young men are still growing in  height until 22, 23, 24, even 25. Yeah, a little bit. Most of it is over. 

But, for instance, I have a daughter who's going to be 20 in a few months. She stopped  growing in height basically by 17. She has a boyfriend.

Every time I see him, he's taller  and he's going to be 20 next birthday as well. Why is it that it's later for men than women? Boys and girls do have different patterns of  physical growth and maturation.

Boys actually become, we can say fertile. They could produce  fertile spermatozoa by about age 13 to 14. But those boys still look like little wimps.

No older  woman is going to really be interested in them. Girls, however, look mature.  They start to look like women years before they are fertile.

And they have  what we call secondary sexual development. The patterns of fatness. Breasts, for  instance, are already noticeable to everyone in the social group, but they're  not fertile until about age 18.

The age at first birth of women around the world  and throughout history is about age 19. Now, I know some 12 year olds give birth because  there's a lot of variation in the rate at which that tempo of maturity plays out but so few  cases are recorded that, like the UK census, the United States census doesn't even include  those numbers. There's so few of them.

That's interesting. I think that's a really common misconception. I think generally people  think once you start having a period, that means you're fertile, right?

No.  Turns out probably not for most people. So just because we start our periods at  around 13 it doesn’t necessarily mean we’re reproductively mature.

Women  might not be fertile until about 18. But Amrita and Manju gave birth for the  first time at 22 and 17 respectively, and both felt too young. Could we have evolved to reproduce  before we’re truly ready?

Yeah, that's a great question. We human  beings are a complex and wondrous mix of biological and socio-cultural  factors and you can't separate the two. Biologically, by 20 a woman should be ready  to have a baby.

And it's not a bad time to have a baby if you want one, because  your body is more or less at its prime. But if you are not ready socially or culturally or  economically, or have too many emotional concerns, then it could be a very bad time  for you. And even for the baby.

Mothers who are worried pass on that  worry through stress hormones things like that to their developing  foetus and to their infants. You might remember that our listener  Lynda was interested in when we mature physiologically speaking - culture aside. But as Barry just said, the two  are inextricably entangled.

And that’s what led us to cultural  anthropologist Bonnie Hewlett. When researching adolescence, she  lived with Aka hunter-gatherers in the Central African Republic. They’re an  egalitarian community - they believe all people are equal regardless of age.

So does  maturity look different in their culture? So when a girl has her first period then she begins to learn more deeply these  foundational key cultural values. And it's tied into this biological  development.

Once that begins, she is able to become independent which is a highly regarded value, sacred value,  this sense of autonomy within the family union. But she can build her own hut. She can signal that  she's ready to begin intimate relations with boys.

In the Aka society they have a fierce,  almost sacred belief in the autonomy of the individual. So it's always, always  the individual who chooses you know, when she wants to build her hut,  when he wants to go on a hunt. So could a girl have her first period  and then decide, like, you know what, I'm not going to build my  hut for a couple of years.

I'm good as I am, I don't want things to change. Yeah. Absolutely.

Absolutely. And it may be that  she signals to the boys that she's not interested or she'll have multiple lovers or she'll,  you know, it's absolutely individual choice. That's interesting because, you know,  in so many other parts of the world, it's totally different.

It sort of decided, okay, at 16 you are ready to vote in some places,  say. At 18 you're ready to drink and you're legally an adult and you're completely,  legally responsible for your decisions. It's not the person's decision  about their own maturity.

Yeah. No. Absolutely.

By 10 the Aka children  can fully take care of themselves. They can hunt, they can cook, they can make  medicines to cure their illnesses. In these societies, in this development of  identity and confidence, it begins in infancy, you know, from the moment the child is born, there's respect for that child as an  individual.

Parents don't tell them no. They let them play with machetes. They  let them learn how to play around fire.

They're regarded as an independent person that  can make their own choices. This movement toward identity, toward confidence, toward  maturity, really is set in the time of birth. Do you think we could benefit from perhaps  having more choice in decisions around maturity?

Again, it's a cultural construct. But  I think as we've seen with the Aka, there's different ways of becoming and  there's diversity in the experience of identity formation and the formation  of maturity, whatever that is. And I think, yeah, if we had a better sense of, individual growth and development rather  than society wide "this is what you are when you're 18" or what you should be.

I  don't think that's useful in some ways. Perhaps there is something to be said for being  able to navigate our own path to adulthood. Because we’re all different, biologically  and culturally.

And it’s clear that the two are inseparable. Aka children sound  worlds more mature at 10 than I was at 18. Which made me wonder, does the environment  you grow up in change your psychological maturity?

What happens, say, if that  environment is chaotic or unsupported? Do you grow up faster, or just have to cope  with more stuff with a less mature brain? Here’s neuroscientist Sarah Jane Blakemore again.

That's a really good question. And both of  those things are probably true. So first of all we know that the developing brain, so  the brain in childhood and adolescence is particularly plastic and changeable, which  means that childhood and adolescence is a sort of sensitive period of brain  development, whereby the brain is particularly susceptible to being moulded and  shaped by the environment it's growing up in.

And if that environment can be positive, but it  can also be negative and that for sure will affect the brain the way the brain develops. We know that  from a lot of animal research, but we also know from recent research on development of the human  brain. But equally the second suggestion is also right, that being exposed to different pressures  at a young age means that you're having to cope with lots of different responsibilities when your  brain isn't at a level of maturity that maybe it should be to cope with those pressures,  and that will affect the way you develop.

So not only does our brain determine  how we behave in our environment, our environment can actually shape our brain. Which reminds me of listener Lynda’s defining  experience as a young university student, trying (and failing) to decide between walking out of a  lecture and striking or staying put and learning. I wondered what Sarah Jayne made of this story.

It's not a simple decision. You have to be  thinking about, you know, the counterfactuals. You have to be thinking about the consequences  of your actions.

Also the social consequences, what your peers will think about you.  There may be pressure to follow them. What the lecturer will think about you.

There may  be negative repercussions of making that decision, other kinds of future repercussions. It's  not a simple decision for actually anyone to make at any age, but certainly at the  age of 18. I mean, I think, you know, most of us remember being 18 and would agree that  we were not our fully mature selves at that age.

Lynda I hope that helps you stop beating  yourself up about your adolescent decision paralysis. But it makes sense that it felt like  a turning point because our brains are plastic, that moment itself could’ve  contributed to you growing up. You wanted to know why 18 is  the legal age of maturity.

Well the answer is slightly unsatisfying.  It’s because we decided it is. Science doesn’t entirely back it up - there is  no overnight transformation on your 18th birthday.

Some of us might have reached  full maturity by then but others may have a full decade to go. Ideally we’d all have  our own “coming of age” age but that could make it kinda complicated to decide  who can vote… or run for President. Thanks so much for getting in touch  Lynda, over to you for the credits.

That's all for this episode  of CrowdScience. If you have a question you would like the team to look into  please email us at crowdscience@bbc. co.

uk. This programme was presented by Caroline Steel and produced by Richard Walker.  Thanks for listening.

Bye.